I have a 1997 GMC 1500, 2 wd with an automatic transmission. I just got it rebuilt about a week ago and the transmission is supposed to be good up to 500 horses, beast sunshell intalled, corvette servo, stronger clutches, boost valve, shift kit, TCI stall converter 2200 max stall . It drives excellent under cruising conditions, but when i get ready to race, ill put it in 1st gear, stall up and take off it just acts like its slipping and wont get above 3000 rpm and then ****s to 2nd gear and fine from there. If i leave it in 3rd and stall and leave, it seems a little sluggish out of 1st but goes all the way through the rpm band and shifts fine from there. also when im highway speed and i want to pass someone, it kicks down but it goes up and down in rpm, varying about 1000 rpm a few times and then will take off, any ideas on what is going on?